Fair Value Measurements - Other Real Estate Owned and Repossessed Assets (Details) - Nonrecurring - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Total Fair Value
Fair Value Measurements
Impaired loans	$ 3,127	$ 2,850
Other real estate and repossessed assets	13,537	13,239
Total Fair Value | Commercial, financial, and agricultural
Fair Value Measurements
Impaired loans	1,263	1,369
Total Fair Value | Commercial real estate | Construction
Fair Value Measurements
Impaired loans	151	0
Total Fair Value | Commercial real estate | Mortgages
Fair Value Measurements
Impaired loans	233	595
Total Fair Value | Residential real estate | Mortgages
Fair Value Measurements
Impaired loans	1,480	886
Total Fair Value | Installment and other consumer
Fair Value Measurements
Impaired loans	0	0
Total Gains (Losses)
Fair Value Measurements
Gains (losses) on impaired loans	0	(57)
Gains (losses) on other real estate owned and repossessed assets	(106)	1
Total Gains (Losses) | Commercial, financial, and agricultural
Fair Value Measurements
Gains (losses) on impaired loans	0	0
Total Gains (Losses) | Commercial real estate | Construction
Fair Value Measurements
Gains (losses) on impaired loans	0	(27)
Total Gains (Losses) | Commercial real estate | Mortgages
Fair Value Measurements
Gains (losses) on impaired loans	0	(20)
Total Gains (Losses) | Residential real estate | Mortgages
Fair Value Measurements
Gains (losses) on impaired loans	0	0
Total Gains (Losses) | Installment and other consumer
Fair Value Measurements
Gains (losses) on impaired loans	0	(10)
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value Measurements
Impaired loans	0	0
Other real estate and repossessed assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Commercial, financial, and agricultural
Fair Value Measurements
Impaired loans	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Commercial real estate | Construction
Fair Value Measurements
Impaired loans	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Commercial real estate | Mortgages
Fair Value Measurements
Impaired loans	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Residential real estate | Mortgages
Fair Value Measurements
Impaired loans	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Installment and other consumer
Fair Value Measurements
Impaired loans	0	0
Other Observable Inputs (Level 2)
Fair Value Measurements
Impaired loans	0	0
Other real estate and repossessed assets	0	0
Other Observable Inputs (Level 2) | Commercial, financial, and agricultural
Fair Value Measurements
Impaired loans	0	0
Other Observable Inputs (Level 2) | Commercial real estate | Construction
Fair Value Measurements
Impaired loans	0	0
Other Observable Inputs (Level 2) | Commercial real estate | Mortgages
Fair Value Measurements
Impaired loans	0	0
Other Observable Inputs (Level 2) | Residential real estate | Mortgages
Fair Value Measurements
Impaired loans	0	0
Other Observable Inputs (Level 2) | Installment and other consumer
Fair Value Measurements
Impaired loans	0	0
Significant Unobservable Inputs (Level 3)
Fair Value Measurements
Impaired loans	3,127	2,850
Other real estate and repossessed assets	13,537	13,239
Significant Unobservable Inputs (Level 3) | Commercial, financial, and agricultural
Fair Value Measurements
Impaired loans	1,263	1,369
Significant Unobservable Inputs (Level 3) | Commercial real estate | Construction
Fair Value Measurements
Impaired loans	151	0
Significant Unobservable Inputs (Level 3) | Commercial real estate | Mortgages
Fair Value Measurements
Impaired loans	233	595
Significant Unobservable Inputs (Level 3) | Residential real estate | Mortgages
Fair Value Measurements
Impaired loans	1,480	886
Significant Unobservable Inputs (Level 3) | Installment and other consumer
Fair Value Measurements
Impaired loans	$ 0	$ 0